The present invention is related to a method of implementing on screen display (OSD) function and a device thereof, and particularly to a method of implementing on screen display (OSD) function and a device thereof by using a dynamic random access memory (DRAM).
On screen display (OSD) function is basically implemented for showing the important information, e.g. Time, TV channel, and Video Setting, for the users on the screen. According to the prior art of implementing OSD function, the read-only-memory (ROM) is usually used for storing the graphic data. Certainly, the desired shown graphic data must be written into the ROM in advance, and which can then be read out from the ROM when one desire to show the graphic data on a screen. However, the graphic data stored in the ROM can""t be changed any more, therefore the method of implementing OSD function according to the prior art have some disadvantages as follows.
(a) The memory space of the ROM used for storing the graphic data is large, therefore the manufacturing cost of the ROM is high. If we desire to lower the manufacturing cost of the ROM, the number of the characters stored in the ROM would be limited.
(b) The characters stored in the ROM can""t be changed from one font to another font.
(c) The displaying position of the graphic data on the screen can""t be moved.
The present invention not only solves the problems as mentioned above, but also provides a method of storing the graphic data in a dynamic random access memory (DRAM) for implementing OSD function.
An object of the present invention is to provide a method and a device of implementing on screen display (OSD) function for lowing the manufacturing cost.
Another object of the present invention is to provide a method and a device of implementing on screen display (OSD) function for improving the flexibility of changing the fonts.
A further object of the present invention is to provide a method and a device of implementing on screen display (OSD) function for easily moving the displaying position of the graphic data on the screen.
According to the first aspect of the present invention, a method of implementing on screen display (OSD) function is provided. The method comprises the steps of storing the graphic data in a dynamic random access memory (DRAM), obtaining the displaying information and a sequence for the graphic data by an OSD decoder, and showing the graphic data by an address generator on a screen according to the displaying information and the displaying sequence.
Preferably, the graphic data is composed of a plurality of characters.
Preferably, the dynamic random access memory (DRAM) is a local dynamic random access memory (DRAM) of a graph-showing device.
Preferably, the graph-showing device is a MPEG decoder.
Preferably, the graphic data is stored in the unused and fractional memory space of the dynamic random access memory (DRAM).
Preferably, the displaying information includes the displaying position, the displaying color and the displaying number of the characters, and the height of the displaying region for the graphic data on the screen.
Preferably, the address generator is a static random access memory (SRAM).
According to the second aspect of the present invention, a device of implementing on screen display (OSD) function is provided. The device comprises a dynamic random access memory (DRAM) for storing the graphic data, an OSD decoder for obtaining a sequence according the stored graphic data, and an address generator electrically connected to the DRAM and the OSD decoder for showing the graphic data on a screen according to the sequence.
Preferably, the graphic data is composed of a plurality of characters.
Preferably, the dynamic random access memory (DRAM) is a local dynamic random access memory (DRAM) of a graph-showing device.
Preferably, the graph-showing device is a MPEG decoder.
Preferably, the graphic data is stored in the unused and fractional memory space of the dynamic random access memory (DRAM).
Preferably, the address generator is a static random access memory (SRAM).
According to the third aspect of the present invention, a method of storing the graphic data in a dynamic random access memory (DRAM) for implementing OSD function is provided. The method comprises the steps of dividing each graphic data into a plurality of lines, arranging the corresponding same lines of each graphic data into the corresponding same pages respectively and producing a plurality of corresponding pointers thereinto for pointing the addresses of next pages to link the plural pages, and storing the plural pages in the unused and fractional space of the dynamic random access memory (DRAM).
Preferably, the graphic data is composed of a plurality of characters.
Preferably, the dynamic random access memory (DRAM) is a local dynamic random access memory (DRAM) of a graph-showing device.
Preferably, the graph-showing device is a MPEG decoder.